An Ultra-Wideband Spatial Filter for Time-of-Arrival Localization in Tunnels

An ultra-wideband (UWB) spatial filter is proposed to mitigate multipath effects in a one-way time-of-arrival (TOA) localization system that localizes along one dimension inside a tunnel. The spatial filter is a two-dimensional weighted array of judiciously placed antennas that exploits the fact that electromagnetic waves propagate as modes in a tunnel by selectively extracting these mode(s). The design of several spatial filters is presented alongside vigorous analyses to characterize the localization performance afforded by them in a noisy environment. The filters are evaluated using data from an analytical equation waveguide model, a ray tracer model and measurements. These spatial filters deliver accurate localization estimates across distance and well-designed filters can operate at higher signal-to-noise ratios (SNRs) than single sensors and their performance is comparable to basic time-reversal (TR) systems. Moreover, the use of the spatial filter in the localization system allows for relatively simple signal processing of received signals in comparison to alternative receiver architectures, such as Rake and TR. Insights into successful spatial filter design are provided in this contribution and this spatial filtering technique has created a new branch of multipath-aware localization systems.